1. Technical Field
The present invention relates to an optical position detecting apparatus that optically detects the position of a target object in a detection region and a display device with position detecting function including the optical position detecting apparatus.
2. Related Art
In recent years, in electronic apparatuses such as a car navigation system, a personal computer, a ticket machine, and a bank terminal, a display device with position detecting function in which a touch panel is arranged on a front surface of an image generating device such as a liquid crystal device is used. In such a display device with position detecting function, a user inputs information while referring to an image displayed on the image generating device. Such a touch panel is configured as an optical position detecting apparatus for detecting the position of a target object in a detection region (see, for example, U.S. Pat. No. 6,927,384).
The optical position detecting apparatus described in U.S. Pat. No. 6,927,384 is an optical type. A light transmitting plate is provided on an input operation side with respect to a direct-view display panel such as a liquid crystal panel. Alight source, a light receiving element, and the like are arranged on the opposite side of the input operation side with respect to the light transmitting plate. Position detection light emitted from the light source is emitted to the input operation side via the light transmitting plate and the position detection light reflected on the target object is received by the light receiving element.
The inventor proposes, for example, an optical position detecting apparatus schematically shown in FIGS. 16A and 16B making practical use of the technique described in U.S. Pat. No. 6,927,384. In the optical position detecting apparatus having such a configuration, light sources for position detection 12 (light sources for position detection 12A to 12D) form an intensity distribution of position detection lights in an in-plane direction of a detection region 10R. A photodetector apparatus 15 detects the position detection lights reflected by a target object Ob in the detection region 10R. A light intensity distribution of position detection light emitted from a light guide plate 13 to the detection region 10R is different between the time when position detection light L2a is emitted from the light source for position detection 12A and the time when position detection light L2b is emitted from the light source for position detection 12B. Therefore, if light reception results in the photodetector apparatus 15 at the time when the position detection light L2a is emitted and at the time when the position detection light L2b is emitted are compared, the position of the target object Ob in a direction indicated by an arrow A can be detected. If light reception results in the photodetector apparatus 15 at the time when position detection light L2c is emitted from the light source for position detection 12C and at the time when position detection light L2d is emitted from the light source for position detection 12D are compared, the position of the target object Ob in a direction indicated by an arrow B can be detected.
However, in the optical position detecting apparatus having the configuration shown in FIGS. 16A and 16B, the position of the target object Ob is detected according to one physical value (light reception intensity) detected by the photodetector apparatus 15. Therefore, when plural target objects Ob are present in the detection region 10R and a light reception amount in the photodetector apparatus 15 increases, the optical position detecting apparatus detects in error that the positions of the target objects Ob are closer to the light sources for position detection 12 than actual positions of the target objects Ob. The configuration shown in FIGS. 16A and 16B is a reference example of the invention and is not a related art.